Maryland independent. [volume] (Port Tobacco, Md.) 1874-current, 1887-03-11
MECHANICAL.


SOME time ago experiments vero
made to ascertain the proportion OF
oxygen in the river Thames at low
water, it being found that as 1t runs
through London, the quantity OF oxy'
gen diminshes a. compared with the
proportion it contains at Richmond
about twelve or thirteen tons of oxygen
being lost between Richmond Bridge
and Somerset House. Recent tests OF
the Thames water show that near the
sewage outfall it contains but about
half a cubic inch of oxygen per gallon,
instead of two cubic inches per gallon,
as above the city; but lower down the
proportion of oxygen rises again untn
the water is within ten per cent. OF lts
richness in oxygen at Richmond. Thus
the considerable power which flowing
water possesses of keeping itself sweet
and clean IS regarded as positively
proved, though the power, great as 1t
Is, may be and often is oyertaxed wheu
the organic matter is non-living. As
to whether it has the power of destroy
ing those minute living organisms
which are the germs of certain dis
eases, different opinions exist among
scientists.
THE quality of good slate is that
it should cleave readily, that the lam.
INN should be straight and unmixed
with foreign substances, and the more
finely laminated it is the larger plates
will be obtained Slate for roofs should
be dense and not porous, and it is best
judged, like other stoSes, by the sharp
ness of the sound. orous plates are
bad, because they swallow water. Sui.
phur is n dangerous ingredient, and
sometimes exists in particles so minute
as to he imperceptible. This mineral
when mixed with water produces Wit
riolic acid and so promotes decompo'
sition. To detect Its presence heat the
S ate with wood embers, and if it exists
it will give forth sulphurous smell.
Oxide of IRON mixed with slate has ?
sympathy for air and water, and so in.
creases the quantity Of oxide or rust
Calcareous matter is equally injurious,
and NAV be tested by observing wheth'
er it pulls up when exposed to muriatiC
acid. Carbonaceous or coaly matter
may he detected by burning. With re
gard to its color, yellow or black spots
indicate the presence Of oxide, arC
black that Of carbonaceous matter. r.
Mechanical JVorid
VICE President CHANUL, in his ad
dress before the mechanical section o
the American Association, considered
what might be called the evolution Of
inventions. Nothing, he said, is more
remarkable than the multitude of minds
and facts which are required for the
perfecting of even a simple machine
or how little the last man may need tC
add to complete the invention. Fact
and natural laws. known for years a.
curiosities are taken mp by some in
ventOr, who fails in the attempt t
render them of practical use; then
second genius takes hold, and profit
ing by the mistakes Of the first, pro
duces at great cost a working machine
Then comes the successful man, who
works out the final practical design
and, whether making or losing q for
tune, vet permanently benefits man
kind. This course is exemplified il
the address by the relation of the
growth of the steam engine; and 81
with other inventions. The steamboa
was being developed from l7C0 to 1907
the locomotive from 1902 to 1929; thu
telegraph from 1929 to 1874; the sew
ing machine, with its 1000 patents
from 1880 to 1850, and the reapine
machine for seyenty-five years, the las
successful man adding b little to tn
work Of his forerunners. The rule ha
been that the basis of success lay in
thorough acquaintance with what hat
been done before, and in setting abou
improvement in a thoroughly scientf
way. "-Poptlar Science Mo3thIB.